1 Field of the Invention
This invention relates generally to systems for monitoring the blood pressure of a patient, and more particularly, to an integrated, blood-pressure transducer assembly for inclusion in such systems.
2 Status of Prior Art
It is common practice to provide in a hospital or other facility in which a patient is being treated, a system adapted to continuously measure and monitor the patient""s blood pressure. In a typical system of this type, the pressure exerted on a column of liquid that communicates with the patient""s blood stream via a catheter implanted in an artery or vein of the patient is sensed by a pressure-sensitive transducer which generates an electrical signal that varies as a function of blood pressure. This signal is conveyed to a monitor on whose screen is displayed He waveform of the signal. And the signal may also be recorded on a print chart to provide a record of the changing blood pressure of the patient in the course of a hospital stay.
The liquid column is derived from an IV bag supported at an elevated position adjacent the patient, the bag containing a saline liquid gravity fed by a supply line to the catheter from which it enters the blood stream. Hence the pressure of the blood is exerted on the liquid column. In practice, a pressurized source of a saline or other liquid may be used, in which event there is no need to elevate the bag.
It is essential hat the liquid flow continuously at a low drip raze in order to keep open the supply line and the catheter. Should the end of the catheter become occluded because of a blood clot or thrombosis, the system would then produce an erroneous blood-pressure reading. The reason therefore that it is vital to maintain a continuous flow of the saline solution through the catheter is in order to avoid the formation of blood clots. Also it is vital that the system be purged of air bubbles.
Air bubbles are compressible and therefore give rise to an uncertain pressure differential between the patient""s blood stream and the pressure transducer, thereby resulting in a measurement error. Moreover, one cannot tolerate the entry of air bubbles into the blood steam, for his may have serious consequences. it is known in the prior art (see U.S. Pat. Nos. 4,464,179 and 4,291,702) to provide a flush valve assembly to facilitate flushing the line in a blood-pressure monitoring system and to establish a proper drip flow rate of the liquid flow after the flushing action is completed. Flushing devices are used when starting and then maintaining the operation of the blood-pressure monitoring system in which medical personnel must flush the pressure measuring apparatus and the line coupled thereto to eliminate therefrom air or gas bubbles.
Of particular background interest is U.S. Pat. No. 4,934,375 which discloses a complete blood-pressure measuring system in which a saline solution for intravenous infusion is contained in an elevated bag from which it flows through a supply line into the inlet port of a valve, the outlet port of which is coupled by the line to a catheter implanted in a blood vessel in the patient being treated.
Another valve port is coupled by a line to an external pressure sensitive transducer whose electrical signal is conveyed by a cable to a monitor. This monitor displays on its screen the waveform of the signal that represents the varying blood pressure of the patient.
In the arrangement disclosed in U.S. Pat. No. 4,934,375, the components which together create the monitoring system are separated from each other, making it necessary when the system is to be put to use, for medical personnel to then assemble the components. To reduce the need for such an assembly operation, there is disclosed in U.S. Pat. No. 4,545,389 a pressure-responsive sensor incorporated in a unitary assembly with the valve. But other components necessary to the system are not included in this assembly.
In the flush devices for a blood-pressure monitoring system disclosed in U.S. Pat. Nos. 3,675,891 and 4,464,179, there are two separate channels for liquid flow. One is a continuous flow channel and the other a purge or fast flush channel. The continuous flow channel has a small bore that functions as a capillary, whereas the fast flush channel has a substantially larger diameter. Instead of a glass capillary tube to restrict flow, a capillary bore may be laser-drilled in the continuous flow channel.
A conventional system for monitoring blood pressure usually is composed of the following three units which normally are separately manufactured and then intercoupled to create the required assembly:
Unit I. This is a pressure sensing unit in which a pressure-sensitive transducer converts the blood-pressure level of a patient into a corresponding electrical signal which is conveyed to a monitor.
Unit II. This unit includes a fast-flush valve which when actuated effects a fast flush of the system to clear it of deleterious air bubbles. Also included is a flow restrictor to maintain at a slow flow rate the liquid being intravenously infused into the patient""s blood stream.
Unit III. This unit includes a stopcock adapted to selectively direct flow to out priming, zeroing and blood sampling operations.
Because units I, II and III are separately manufactured, in order to produce an assembly thereof for installation in a blood-pressure measuring system, these units must be joined together by suitable bonding agents or by UV curable bonds. Not only does his add appreciably to manufacturing costs but it also may result in a defective assembly in that the bonded junctions of the units may crack and not be leak proof.
In view of the foregoing the main object of this invention is to provide a unitary blood-pressure transducer assembly to be included in a blood-pressure monitoring system, the assembly having a common casing which integrates three sub-assemblies.
More particularly, an object of this invention is to provide a unitary assembly of the above type which integrates a first sub-assembly that includes a pressure sensor, a second sub-assembly that includes a fast-flush valve, and a third sub-assembly that includes a stop cock.
An invasive blood-pressure monitoring system that includes a transducer assembly in accordance with the invention, though not costly or difficult to install, nevertheless makes a significant contribution to the diagnosis of a patient""s condition as well as to a treatment appropriate to this condition. A sudden shift in the cardiovascular condition of a patient can be quickly identified by the system and may make possible a prompt, life-saving intervention.
A proper diagnosis of the condition of a patient is aided when the varying blood pressure of the patient is converted into a waveform that is displayed by a monitor. And the system is capable also of monitoring a patient""s response to drug therapy to determine whether the dosage being administered to the patient needs to be adjusted to enhance the effectiveness of the therapy.
Among the significant advantages of an assembly in accordance with the invention are the following:
A. The assembly is easy to install, for all that is necessary is to interpose the assembly in the supply line running from an elevated bag containing a saline solution to a catheter implanted in a blood vessel of the patient.
B. The costs of manufacturing the assembly are low as compared to the expenses incurred when the sub-assemblies are separately manufactured and then joined together.
C. Because the unitary assembly is not composed of separate sub-assemblies which are bonded together, the assembly is free of cracks and other defects.
D. The orientation of the adjustable parts of the assembly which must be manipulated by personnel operating the system is such as to facilitate such manipulation.
E. Because the casing of the assembly is molded of transparent plastic material, blood as well as air bubbles which are potentially dangerous, are exposed.
Briefly stated, these objects are attained in a unitary blood-pressure transducer assembly for inclusion in a system adapted to monitor the blood pressure of a patient while the patient is being supplied with a saline or other liquid through a supply line leading to a catheter implanted in a blood vessel. The assembly includes three sub-assemblies housed within a common casing and having an inlet port to be coupled to the upstream section of the line and an outlet port to be coupled to the downstream section thereof whereby the liquid flows through the assembly. Intermediate the ports is a first sub-assembly having a transducer that senses the pressure of a column of liquid developed within the assembly whose pressure varies as a function of the pressure of the blood streaming through the blood vessel.
Adjacent the inlet port is a second sub-assembly that includes a fast-flush valve to purge air bubbles from the assembly and a flow restrictor to maintain liquid flow at a low flow rate. The third sub-assembly which is adjacent the outlet port includes a stopcock to selectively direct flow to allow for priming and zeroing of the system as well as blood sampling.